Hold a level horizontally against the wall studs to identify any bowed more than 1/8 inch. Mark any bowed studs with a marker.
Hold the level vertically along the bowed stud and draw a straight line to mark the warped wood to remove.
Run the power plane steadily over the bowed wood and shave off excess wood, using the marked line as a depth guideline. Double-check the work with the level to see if you need to take off any more wood.
Hold the level horizontally along the wall studs and mark any that bow more than 1/2 inch.
Cut a series of evenly spaced kerfs, 1 3/4 inches deep and 10 inches apart, along the bowed section of the stud with a circular saw. Do not cut kerfs beyond the bowed section on the stud.
Toe-nail a nail at a sharp angle downward through each kerf and pound it gently with a hammer. The cut tightens with each tap on the nail, straightening the bowed section on the stud. Continue hammering nails through the kerfs until the stud straightens.
Measure the length of the repaired section of the stud. Cut a piece of 1-inch lumber, either 1 by 2 or 1 by 3, to the measured length. Screw this lumber to the repaired section of stud to reinforce the repair.